Method of filling aquiferous boreholes with explosives

ABSTRACT

In a method of filling aquiferous boreholes with a powdered ammonium nitrate explosive containing swelling and waterrepellentizing agents which is uncartridged by means of a gaseous propellant from a pressure tank through a conduit, the improvement which comprises feeding said explosive composition to said aquiferous borehole through an orifice positioned toward the bottom of the borehole and thereafter step-wise or continuously withdrawing from the bottom such orifice from such conduit such that the orifice is located no more than 50 cm above the surface of the delivered explosive and below the surface of the water in the borehole.

United States Patent [1 1 Christmann et al.

[ 1 NOV. 25, 1975 [73] Assignee: Dynamit Nobel Aktiengesellschaft,

Troisdorf, Germany 22 Filed: Aug. 27, 1973 [21] Appl. No.: 391,722

[30] Foreign Application Priority Data 3.377.909 4/1968 Grant et al. 86/20 C 3.640.784 2/1972 Yancik ct all i 149/21 3.781.180 12/1973 Harrison et al. 149/21 FOREIGN PATENTS OR APPLICATIONS 119.515 5/1970 Norway Primary E.\aminerSamuel Feinberg Assistant Emminer-l-larold Tudor Attorney Agent, or Firm-Burgess. Dinklage & Sprung [57] ABSTRACT In a method of filling aquiferous boreholes with a powdered ammonium nitrate explosive containing swelling and water-repellentizing agents which is uncartridged by means of a gaseous propellant from a pressure tank through a conduit. the improvement which comprises feeding said explosive composition to said aquiferous borehole through an orifice positioned toward the bottom of the borehole and thereafter step-wise or continuously withdrawing from the bottom such orifice from such conduit such that the orifice is located no more than 50 cm above the surface of the delivered explosive and below the surface of the water in the borehole.

12 Claims, N0 Drawings METHOD OF FILLING AQUIFEROUS BOREHOLES WITH EXPLOSIVES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention is directed to a process of filling boreholes with explosives. More particularly, this invention is directed to a method of filling an aquiferous borehole with a powdered ammonium nitrate type explosive whereby water need not be removed prior to the time that the explosive composition is introduced into the borehole. Still more particularly, this invention is directed to a process wherein in a one-step operation a borehole is charged with an explosive composition, and water present in said borehole is displaced upwardly toward the entrance to such borehole.

2. DISCUSSION OF THE PRIOR ART It is known in the prior art to blow powdered ammonium nitrate explosives in the uncartridged state into boreholes by means of compressed air. The application of this method has hitherto required that the boreholes be dry or not too moist and that no water flow afterward into the area of the borehole. If this requirement is not met, it must be expected that the blasting work willproduce poor results. Warnings have therefore always been given against blowing uncartridged explosives into boreholes containing water. It has therefore been found necessary to use so-called slurries for filling aquiferous boreholes with uncartridged explosives. These water-containing mixtures, however, have a much poorer detonability than the water-free mixture. The work capacity of the aqueous mixture in relation to weight is considerably less than that of the water-free mixture. The problem, therefore, existed of finding a method making it possible to fill aquiferous boreholes with powdered, uncartridged explosives.

SUMMARY OF THE INVENTION Broadly, this invention contemplates an improvement in a method of filling aquiferous boreholes with (l explosives (2) wherein the explosives are carried by a gaseous propellant, said improvement comprising delivering said explosive to the bottom of said borehole by means of a gaseous propellant and during the filling process withdrawing from the borehole in a step-wise or continuous manner, the orifice from which said propellant and said explosives emanate so as to position the orifice above the surface of the delivered explosive and below the surface of the water in the borehole.

In a particularly desirable embodiment the present invention contemplates an improvement in a method of filling aquiferous boreholes with (l) explosives (2) by use of a gaseous propellant from a pressure tank through a conduit, said improvement comprising positioning the orifice of said conduit toward the bottom of the borehole and during the filling of said borehole with said explosive step-wise or continuously withdrawing said orifice from the borehole such that the orifice is positioned no more than 50 cm above the surface of the delivered explosive and below the surface of the water in the borehole. Preferably, the orifice from which the explosive and propellant emanate is positioned no more than cm above the surface of the delivered explosive.

It has been found, in accordance with the present invention, that boreholes that are initially filled with water can be filled with explosives such as powdered ammonium nitrate explosives without removing the water prior to the filling operation. Thus, in accordance with the invention, it has been found that a powdered ammonium nitrate explosive can be propelled into an aquiferous borehole by the use of compressed air. The orifice from which the ammonium nitrate explosive and compressed air are discharged is positioned no more than 50 cm above the surface of the bottom of the borehole. As the borehole is filled with ammonium nitrate explosive or other explosive, the orifice is stepwise or gradually removed so that it is positioned no more than 50 cm above the surface of explosive already placed in the borehole. Preferably, it is positioned no more than 10 cm above the surface of the explosive within the borehole. The air discharged from the hose orifice during the injection and filling operation has been found to result advantageously in a virtual partition between the explosive and the water above it. The method of the present invention'can therefore easily be applied to boreholes completely filled with water. Particularly advantageous is the great degree to which the borehole can be filled with explosive offsetting the small technical expenditure required for good lasting power.

The invention has been described above as being applicable to powdered explosives (l) broadly. It is particularly contemplated to use as the explosive an ammonium nitrate explosive alone or in admixture with other substances such as an aluminum powder, a mineral oil and the like. Additionally, the invention has been described as employing a gaseous propellant which propels the explosive into the borehole at the bottom thereof, which gaseous propellant lifts the water in the aquiferous borehole. While any number of different gaseous propellants, including the halogenated alkanes, can be employed for this purpose, it is, of course, preferable to use a readialy available, inexpensive gaseous propellant. Nitrogen and air are particularly contemplated.

The withdrawal of the hose in the method of the invention can be performed easily and in a simple manner, since the operator can easily feel from the slight vibration of the hose as the explosive flows through it whether the explosive is still freely flowing or whether the amount flowing through is diminishing because the level of the explosive rising in the borehole is approaching too closely to the hose orifice, thereby impairing the discharge of the explosive from the hose. In the latter case the hose is then simply withdrawn by a certain amount so that the explosive again flows freely. At the same time it is easily possible to assure the perfect flow of material in the hose by appropriate automatic devices, such as a microphone mounted on the hose and containing a system for the automatic withdrawal of the hose.

DESCRIPTION OF PREFERRED EMBODIMENTS Up to 50% by weight of the ammonium nitrate may be replaced by other oxygen-yielding salts, such as nitrates or perchlorates of the alkali or alkaline earth metals, for example. Also, these oxygen-yielding salts should, like the ammonium nitrate, be in a grain shape and fineness which will assure easy air injection.

Examples of water-repellentizing agents which can be included together with the ammonium nitrate or other explosive include polyvalent salts of long-chain fatty acids and/or long-chain fatty amines or salts thereof. The expression long-chain is to be underployed together with a water-repellentizing agent. Such repellentizing agents can be present in the explosive in the absence of the swelling agent.

Lubricants, such as graphite of molybdenum disulfides, for example, may also be added to the explosive. The powdered ammonium nitrate explosives can contain combustible substances, such as mineral oil or diesel oil, nitrotoluenes, coal dust, glycol, urea, wood flour or vegetable flour. They can also contain metallic combustibles such as aluminum, magnesium or alloys of that nature.

The ammonium nitrate explosives named are already known as such on the basis of the nature and quantity of their composition for use in cartridge form, the cartridge casing, along with the action of the swelling agents and/or water-repellentizing agents, providing substantial protection against the penetration of water into the explosive The use of the cartridge casing was the only factor that made it possible at all to use powdered ammonium nitrate explosives in aquiferous boreholes. It has the disadvantage, however, that complete filling of the borehole or full utilization of the borehole volume for the explosive cannot be achieved.

In the process of the present invention, it has proven advantageous with regard to economy, behavior in relation to water, and the performance of the explosive to use explosives consisting of 60 to 98 weight percent ammonium nitrate and 2 to 40 weight percent combustible substances, the combustible substances containing up to 10 weight percent (with respect to the explosive) of swelling agent and/or up to 3 weight percent (with respect to the explosive) of water-repellentizing agents.

It has been found that when ammonium nitrate is used in prilled form it is easy to blow in but the moisture absorption is not satisfactory under all circumstances. When ammonium nitrate is used in ground form only, the moisture absorption is low, but when it is injected by blowing irregularities may occur in the transport of the explosive through the hose. It has therefore proven to be advantageous if, according to a further proposal of the invention,-the ammonium nitrate content of the explosives is present both in prilled form and in ground form, preferably in a weight ratio of between 5:1 to 1:5, most preferably 2:1. Prills can be used in mesh sizes of'0.2 to mm, preferably 0.2 to 6 mm, and especially 0.8 to 2.5 mm.

For the operation of blowing the explosive into boreholes the last section of the hose can be replaced by a pipe. Holes can be provided laterally at the end of the hose or pipe so that part of the air escapes through them and promotes the displacement of the water. An annular bead can also be provided at the end of the hose to aid the pushing of the hose out of the borehole by the delivered explosive on the one hand, and on the other hand, to additionally favor the displacement of the water as a result of the higher velocity of the air jet between the bead and the wall of the borehole.

It has furthermore been found that increasing the air blast pressure to about 4 kp/cm results in a reduction of the moisture absorption of the explosive being blown in. Operating at higher blast pressures achieves no important additional advantages in ordinary applications, although it is also practicable. Generally the pressure of the propellant e.g. air is between 0.5 and 10 kp/cm excess-pressure. The method of the invention can also be utilized to place a higher-energy explosive at the bot tom of the pressure tank and a lower-energy explosive on top of it so that a more powerful explosive will be charged in the bottom of the borehole and a less powerful explosive will be placed above that as the pressure tank empties from the bottom.

If in a particular case it is desired that the bottom end of the explosive column in the borehole be as free as possible of water, one can, according to another embodiment of the invention, pump air or other propellant through the hose into the bottom of the borehole before starting the injection of the explosive, in order to displace as much as possible of the water there present prior to the injection of the explosive. The additional air required for this purpose can be delivered to the hose laterally at an appropriate point.

In order to more fully illustrate the invention and the manner of practicing the same, the following examples are set forth.

EXAMPLE 1 l xffpr this experiment an explosive mixture of the following composition was used:

Aluminum powder 30 weight percent 10 weight percent Mineral oil 2 weight percent Calcium stearate 1 weight percent Guar flour 2 weight percent The mixture was blown'through a 6-meter-long air hose of 25 mm inside diameter from a pressure tank feeding apparatus into a vertical pipe 4.50 m long, with an inside diameter of 80 mm, filled with water. The pipes l consisted in its lower portion of a glass-clear section 2 m long for observation of the charging operation. The working pressure in the pressure tank was 3 kp/cm At this pressure a ratio by volume between solid and air (converted to a pressure of l kp/cm of 1:2 to l:3 was achieved in the charging hose.

During the blowing operation it is necessary that the injection hose be withdrawn as the pipe fills with explosive. When the material being blown into the pipe has risen so far that it reaches the orifice of the blowing hose any further discharge from the hose orifice is blocked. The blowing hose is then gradually drawn out so that a clearance between it and the column of material is created and thus the orifice of the hose is again released. Then the flow of material in the hose is resumed and the filling progresses until the explosive column again reaches the orifices of the hose. A column with a length of 110 cm is placed in the pipe and left standing under a water column of l m. No further water absorption by the explosive. After this period the column had a moisture distribution as follows: At the bottom, i.e., in the area where the blowing began, there was a plug 10 cm long with a 22% water content. Then followed the main column cm long which was produced by continuous blowing, with a water content of4 Between this comparatively dry portion of the charge column and the water column remaining above it there was a wet section cm long with a water contentofl6%. i g r In use in the borehole the comparatively dry explosive portion constitutes virtually the entire charge column, and the short, moist sections at both ends of the charge column take no part in the total explosive mass.

An explosive column with 4% moisture content was introduced in another steel pipe with an inside diameter of 52 mm, a wall thickness of4 mm and a length of 450 mm. (1) upon ignition by means of a booster charge consisting of 27 g of pentaerythritoltetranitrate and 3 g of wax (density 1.5 g/cm). A plug with a moisture content 50 mm long and one with 13% moisture content and I00 mm long deliberately interposed by way of experiment did not interfere with the detonation by the booster charge.

The same explosive mixture was also blown through a 23-meter-long hose with a 25 mm inside diameter from the pressure tank charger into a 13.5-meter-long, water-filled pipe whose axis was inclined from the vertical (slanting). The inside diameter was again 80 mm. The bottom end of the pipe was again transparent. The working pressure in the pressure tank amounted to 4 kp/cm In this example, some compressed air was additionally blown into the injection hose at a point below the charging tank in order to further loosen up the material to be transported in the hose. In this manner a volume ratio between the material and the air of 1:4 to 1:5 was achieved.

The blowing-in process in the procedure of Example 1 took place with no friction. If this additional air was used and was injected into the charging hose before the valve on the charging tank was opened, the water in the bottom of the borehole was partially displaced before the explosive emerged from the charging hose. This eliminated the wet, approximately 100 mm long plug of explosive at the bottom of the borehole. The continuously charged explosive column had absorbed a moisture content of only I to 3% in this experiment. Between this comparatively dry explosive column and the water above it there was again a more thoroughly wet explosive column of 100 to 200 mm length.

EXAMPLE 2 An explosive mixture of the following composition was used:

NH.NO;,, prilled 60 weight percent (90 weight-71 grain size between 0.8 and 2.5 mm, balance smaller than 0.8 mm) NH NO ground Mineral oil Calcium stearate Guar flour 34 weight percent 3 weight percent l weight percent 2 weight percent detonated perfectly in the steel pipe described in Ex- 6 ample 1. If the moisture content was deliberately increased to 8% by way of experiment, the mixture in the steel pipe still reacted with detonation.

EXAMPLE 3 An explosive mixture of the following composition was used:

NH NO prilled (9O weight-71 grain size between 0.8 and 2.5 mm. balance smaller than 0.8 mm) 55.5 weight percent NH,NO ground Aluminum powder 31.0 weight percent 5.0 weight percent that was fluid at 0C.

When tested in the same manner as in Example 2, the mixture-when blown in absorbed 4.5% moisture. In the test in the steel pipe, the mixture detonated completely without difficulty. When the moisture content was experimentally increased to 8%, the mixture still reacted with detonation.

What is claimed is:

1. In a method filling an aquiferous borehole with a powdered and uncartridged explosive containing swelling agents and water-repellants employing a gaseous propellant issuing from an orifice positioned at the terminal end of a conduit, the improvement which comprises positioning said conduit toward the bottom of said borehole and, during the filling of said borehole with such gaseous repellant and explosives, stepwisely withdrawing said orifice from said borehole while displacing water upwardly in said borehole by said gaseous propellant and maintaining a clearance between said orifice and any powdered and uncartridged explosive deposited in said borehole, the withdrawal of said borehole being such that the orifice is located no more than 50 cm above the surface of any delivered explosive and below the surface of the water in the borehole.

2. A method according to claim 1 wherein said propellant is compressed air.

3. A method according to claim 2 wherein said orifice is maintained no more than 10 cm above the surface of any delivered explosive.

4. A method according to claim 3 wherein the explosive consists of 60 to 98 weight percent ammonium nitrate and 2 to 40 weight percent of a combustible substance, said combustible substance containing up to 10 weight percent, based upon the weight of the explosive, of a swelling agent.

5. A method according to claim 3 wherein said explosive consists of 60-98 weight percent ammonium nitrate and 2-40 weight percent of a combustible substance, said combustible substance containing up to 3 weight percent, based upon the weight of said explosive, of a water-repellentizing agent.

6. A method according to claim 3 wherein the ammonium nitrate content of the explosive is present in both prilled and in ground form, such that the ratio of the prilled to ground form is between 5:1 and 1:5.

7. A method according to claim 6 wherein theweight ratio of the prilled form of ammonium nitrate to ground form of ammonium nitrate is 2:1.

8. A method according to claim 3 wherein the explosive composition is delivered from a pressure tank which feeds said conduit, which pressure tank is filled with an energy-rich explosive at the bottom thereof and an explosive of lesser energy above said energy-rich explosive whereby, as the pressure tank empties from the bottom, the explosive of greater strength is charged into the bottom of said borehole and the explosive of weaker strength is charged into the portion above said bottom.

9. A method according to claim 3 wherein immediately before the commencement of the injection of the explosive, a gaseous propellant is fed through the conduit into the bottom of the borehole whereby to displace a portion of the water contained therein.

10. A method according to claim 9 wherein said propellant is compressed air.

11. A method according to claim 3 wherein the pressure of the compressed air is between 0.5 and 10 kp/cm excess pressure.

12. In a method of filling an aquiferous borehole with a powdered and uncartridged explosive containing swelling agents and water-repellants employing a gaseous propellant issuing from an orifice positioned at the terminal end of a conduit, the improvement which comprises positioning said conduit toward the bottom of said borehole and, during the filling of said borehole, continuously withdrawing said orifice from said borehole while issuing from said orifice said gaseous propellant and explosive such that there is maintained a clearance between said orifice and any delivered explosive such that water in said borehole is displaced upwardly by said gaseous propellant, the withdrawal of said orifice being such that the orifice is located no more than 50 cm. above the surface of any delivered explosive and below the surface of the water in the borehole.

* l l l 

1. In a method filling an aquiferous borehole wiTh a powdered and uncartridged explosive containing swelling agents and waterrepellants employing a gaseous propellant issuing from an orifice positioned at the terminal end of a conduit, the improvement which comprises positioning said conduit toward the bottom of said borehole and, during the filling of said borehole with such gaseous repellant and explosives, stepwisely withdrawing said orifice from said borehole while displacing water upwardly in said borehole by said gaseous propellant and maintaining a clearance between said orifice and any powdered and uncartridged explosive deposited in said borehole, the withdrawal of said borehole being such that the orifice is located no more than 50 cm above the surface of any delivered explosive and below the surface of the water in the borehole.
 2. A method according to claim 1 wherein said propellant is compressed air.
 3. A method according to claim 2 wherein said orifice is maintained no more than 10 cm above the surface of any delivered explosive.
 4. A method according to claim 3 wherein the explosive consists of 60 to 98 weight percent ammonium nitrate and 2 to 40 weight percent of a combustible substance, said combustible substance containing up to 10 weight percent, based upon the weight of the explosive, of a swelling agent.
 5. A method according to claim 3 wherein said explosive consists of 60-98 weight percent ammonium nitrate and 2-40 weight percent of a combustible substance, said combustible substance containing up to 3 weight percent, based upon the weight of said explosive, of a water-repellentizing agent.
 6. A method according to claim 3 wherein the ammonium nitrate content of the explosive is present in both prilled and in ground form, such that the ratio of the prilled to ground form is between 5:1 and 1:5.
 7. A method according to claim 6 wherein the weight ratio of the prilled form of ammonium nitrate to ground form of ammonium nitrate is 2:1.
 8. A method according to claim 3 wherein the explosive composition is delivered from a pressure tank which feeds said conduit, which pressure tank is filled with an energy-rich explosive at the bottom thereof and an explosive of lesser energy above said energy-rich explosive whereby, as the pressure tank empties from the bottom, the explosive of greater strength is charged into the bottom of said borehole and the explosive of weaker strength is charged into the portion above said bottom.
 9. A method according to claim 3 wherein immediately before the commencement of the injection of the explosive, a gaseous propellant is fed through the conduit into the bottom of the borehole whereby to displace a portion of the water contained therein.
 10. A method according to claim 9 wherein said propellant is compressed air.
 11. A method according to claim 3 wherein the pressure of the compressed air is between 0.5 and 10 kp/cm2 excess pressure.
 12. In a method of filling an aquiferous borehole with a powdered and uncartridged explosive containing swelling agents and water-repellants employing a gaseous propellant issuing from an orifice positioned at the terminal end of a conduit, the improvement which comprises positioning said conduit toward the bottom of said borehole and, during the filling of said borehole, continuously withdrawing said orifice from said borehole while issuing from said orifice said gaseous propellant and explosive such that there is maintained a clearance between said orifice and any delivered explosive such that water in said borehole is displaced upwardly by said gaseous propellant, the withdrawal of said orifice being such that the orifice is located no more than 50 cm. above the surface of any delivered explosive and below the surface of the water in the borehole. 